1. Field of the Invention
The invention relates to a magneto-resistive sensor detecting magnetically recorded data out of a medium having magnetically stored data therein, a method of fabricating the same, and an apparatus for magnetically reproducing data, including the same.
2. Description of the Related Art
There have been known a magneto-resistive sensor (hereinafter, referred to simply as xe2x80x9cMR sensorxe2x80x9d) and a magneto-resistive head (hereinafter, referred to simply as xe2x80x9cMR headxe2x80x9d) for detecting a magnetic field. These sensor and head read magnetically recorded data out of a medium in which data have been magnetically stored, with a high linear density.
On detecting a magnetic field, MR sensor varies its electrical resistance in accordance with intensity and direction of the detected magnetic field. That is, MR sensor detects fluctuation in electrical resistance therein to thereby detect a magnetic field.
MR sensor having the above-mentioned function can be grouped into a sensor which operates on the basis of anisotropic magneto-resistive effect (hereinafter, referred to simply as xe2x80x9cAMRxe2x80x9d) and a sensor which operates on the basis of giant magneto-resistive effect (hereinafter, referred to simply as xe2x80x9cGMRxe2x80x9d). Among GMR, spin-valve effect magneto-resistive effect is well known to those skilled in the art.
An example of AMR type MR sensor is described, for instance, in D. A. Thomson et al., xe2x80x9cMemory, Storage, and Related Applicationsxe2x80x9d, IEEE Trans. on Mag. MAG-11, pp. 1039, 1975.
In AMR type MR sensor, electrical resistance is varied in proportion to Cos2xcex8 wherein xcex8 indicates an angle between an orientation of magnetization in a magnetic layer (MR layer) which orientation is varied in accordance with a magnetic field of a signal, and a direction in which a sense current flows in the MR sensor. AMR type MR sensor is generally designed to include a magnetization-bias layer for applying magnetization-bias to MR layer, in order to suppress Barkhausen noise by suppressing formation of magnetic domain in MR layer. The magnetization-bias layer is formed at opposite sides of a sense region of MR layer, and applies magnetization-bias to MR layer in a direction in which a sense current flows. Such magnetization-bias layer is composed of anti-ferromagnetic material such as FeMn, NiMn and nickel oxide, for instance.
A spin-valve effect type MR sensor, which is one of GMR type MR sensors, is generally designed to include MR layer comprised of a multi-layered structure including two magnetic layers, and a non-magnetic layer sandwiched between the magnetic layers. Since fluctuation in resistance in MR layer is dependent on spin-dependent transmission of conduction electrons between the two magnetic layers sandwiching the non-magnetic layer therebetween, and spin-dependent scattering which occurs at interfacial planes among the layers in association with the spin-dependent transmission, MR layer generates significant magneto-resistive effect. Specifically, electrical resistance in MR layer is varied in proportion to cos xcex8 wherein xcex8 indicates an angle between magnetization orientations of the two magnetic layers.
The spin-valve effect type MR sensor having such a structure as mentioned above has higher sensitivity than that of AMR type MR sensor, and hence, exhibits greater fluctuation in electrical resistance than that of AMR type MR sensor.
Examples of the above-mentioned spin-valve effect type MR sensor are suggested as follows.
Japanese Unexamined Patent Publication No. 2-61572 has suggested a magneto-resistive sensor including a multi-layered structure having a non-magnetic layer, two ferromagnetic layers sandwiching the non-magnetic layer therebetween, an anti-ferromagnetic layer making contact with one of the ferromagnetic layers. The ferromagnetic layers are composed of ferromagnetic transition metals or alloy thereof, and the anti-ferromagnetic layer is composed of FeMn.
Japanese Unexamined Patent Publication No. 4-358310 has suggested a magneto-resistive sensor including a multi-layered structure having a non-magnetic metal layer, and two ferromagnetic layers sandwiching the non-magnetic metal layer therein. The two ferromagnetic layers are designed to have magnetization orientations which are perpendicular to each other when a magnetic field applied thereto has an intensity of zero. Since magnetization orientations are perpendicular to each other when an applied magnetic field is zero in intensity, the suggested magneto-resistive sensor has superior linearity in fluctuation in electrical resistance.
Japanese Unexamined Patent Publication No. 6-203340 has suggested a magneto-resistive sensor including a multi-layered structure having a non-magnetic metal layer, two ferromagnetic layers separated from each other by the non-magnetic metal layer, and an anti-ferromagnetic layer making contact with one of the ferromagnetic layers. The two ferromagnetic layers are designed to have magnetization orientations which are perpendicular to each other when a magnetic field of a signal has an intensity of zero.
Japanese Unexamined Patent Publication No. 7-262529 has suggested a magneto-resistive sensor including a multi-layered structure comprised of a first magnetic layer, a non-magnetic layer, a second magnetic layer, and an anti-ferromagnetic layer. The first and second magnetic layers are composed of CoZrNb, CoZrMo, FeSiAl, FeSi, NiFe alone or in combination of Cr, Mn, Pt, Ni, Cu, Ag, Al, Ti, Fe, Co or Zn.
Japanese Unexamined Patent Publication No. 10-92638 has suggested a magneto-resistive sensor including a multi-layered structure comprised of a non-magnetic substrate, a non-magnetic base layer, a magnetic layer, and a protection film. The non-magnetic base layer is comprised of a multi-layered structure including a first base layer composed of Ta, Ag or Al and a second base layer formed on the first base layer and composed of Cr or alloy of Cr. The magnetic layer is composed of an alloy predominantly containing Co.
In the above-mentioned MR sensors, a base layer is composed of Ta in order to enhance crystallinity of MR layer.
For instance, an example of MR sensor having a base layer composed of Ta is suggested in Abstract of 21st Japan Applied Magnetic Academy Conference, 1997, pp.26.
FIG. 1 is a cross-sectional view of a multi-layered structure of the spin-valve effect type MR sensor suggested in the Abstract. As illustrated in FIG. 1, the suggested MR sensor has a multi-layered structure including a base layer 2, a non-fixed magnetic layer 3, a non-magnetic layer 4, a fixed magnetic layer 5, a magnetization-bias layer 6, and a protection layer 7, deposited on a substrate 1 in this order. The base layer 2 is composed of Ta in order to enhance crystallinity of a portion of the multi-layered structure, comprised of the non-fixed magnetic layer 3, the non-magnetic layer 4, the fixed magnetic layer 5, and the magnetization-bias layer 6.
An apparatus for magnetically reproducing data, including such MR sensor as mentioned above, has been recently required to enhance reproduction output and improve a signal/noise ratio (S/N ratio). To this end, MR sensor has to be designed to have an enhanced resistance-change ratio and enhanced sensitivity.
However, if a base layer is composed of Ta, it is impossible to enhance a resistance-change ratio or MR rate. Hence, a base layer has to be composed of a material other than Ta. However, crystallinity of MR layer would be degraded, if a base layer were composed of a material other than Ta.
In view of the above-mentioned problem, it is an object of the present invention to provide a magneto-resistive sensor including MR layer having crystallinity which is superior to almost the same degree as crystallinity obtained when a base layer is composed of Ta, and enhancing a resistance-change rate (MR rate), even though MR layer is composed of a material other than Ta.
It is also an object of the present invention to provide a method of fabricating such MR sensor, and an apparatus for magnetically reproducing data, including such MR sensor.
In one aspect of the present invention, there is provided a magneto-resistive sensor including (a) a multi-layered structure including a base layer, a magnetic layer, and a non-magnetic layer, the magnetic and non-magnetic layers of being deposited on or above the base layer, the multi-layered structure having a sense region therein, and (b) a pair of electrode layers electrically connected to the sense region at its opposite sides, the electrode layers leading a sense current into the sense region at one side thereof and leading the sense current out of the sense region through the other side thereof, the magneto-resistive sensor detecting a magnetic field of a signal in accordance with fluctuation in a resistance in the sense region, the base layer being composed of zirconium (Zr) or alloy thereof.
For instance, the multi-layered structure may be comprised of (a) a first magnetic layer having magnetization an orientation of which varies in accordance with a magnetic field of a signal, (b) a non-magnetic layer, (c) a second magnetic layer having magnetization an orientation of which is not varied by the signal magnetic field, and (d) a magnetization-bias layer applying the magnetization to the second magnetic layer, the layers (a) to (d) being deposited on the base layer in this order or in the opposite order.
It is preferable that the magneto-resistive sensor further includes at least one magneto-resistance enhancing layer located adjacent to at least one of the first magnetic layer and the second magnetic layer.
For instance, a magneto-resistance enhancing layer may be sandwiched between the first magnetic layer and the non-magnetic layer. As an alternative, a magneto-resistance enhancing layer may be sandwiched between the non-magnetic layer and the second magnetic layer. The magneto-resistive sensor may be designed to include first and second magneto-resistance enhancing layers, in which case, the first magneto-resistance enhancing layer may be sandwiched between the first magnetic layer and the non-magnetic layer, and the second magneto-resistance enhancing layer may be sandwiched between the non-magnetic layer and the second magnetic layer.
The magneto-resistance enhancing layer may be composed of a material selected from a group consisting of Co, NiFeCo, FeCo, CoFeB, CoZrMo, CoZrNb, CoZr, CoZrTa, CoHf, CoTa, CoTaHf, CoNbHf, CoHfPd, CoTaZrNb, CoZrMoNi, and amorphous material.
It is preferable that the magneto-resistance enhancing layer has a thickness in the range of 0.5 nm to 5 nm both inclusive.
It is preferable that the magneto-resistive sensor further includes second magnetization-bias layers formed at opposite sides of the sense region, the second magnetization-bias layers applying magnetization to the first magnetic layer in a direction of the sense current, an orientation of the magnetization being varied in accordance with the signal magnetic field, each of the second magnetization-bias layers making contact with the first magnetic layer.
It is preferable that the alloy of zirconium contains at least one of Ta, Hf, W, Cr, Ti, Mo, Pt, Ni, Ir, Cu, Ag, Co, Zn, Ru, Rh, Re, Au, Os, Pd, Nb and V.
It is preferable that an interface between the base layer and the magnetic or non-magnetic layer, an interface between the base layer and the first magnetic layer, and an interface between the base layer and the magnetization-bias layer all have roughness equal to or smaller than 2 nm.
It is also preferable that an interface between the base layer and the magnetic or non-magnetic layer, an interface between the base layer and the first magnetic layer, and an interface between the base layer and the magnetization-bias layer all have mirror reflectivity equal to or greater than 0.1, more preferably, 0.2.
It is preferable that the magneto-resistive sensor further includes (a) a lower gap layer formed below the multi-layered structure, (b) a lower shield layer formed below the lower gap layer, (c) an upper gap layer formed on the multi-layered structure, and (d) an upper shield layer formed on the upper gap layer.
There is further provided a magneto-resistive sensor including (a) a substrate, (b) a lower shield layer formed on the substrate, (c) a lower gap layer formed on the lower shield layer and composed of electrically insulating material, (d) a magneto-resistive element formed on the lower gap layer, (e) an insulating layer formed on the magneto-resistive element, (f) a pair of magnetization-bias layers formed at opposite sides of the magneto-resistive element, (g) an upper gap layer formed over the magneto-resistive element and the magnetization-bias layers, and (h) an upper shield layer formed on the upper gap layer, the magneto-resistive element including (d1) a multi-layered structure including a base layer, a magnetic layer, and a non-magnetic layer, the magnetic and non-magnetic layers being deposited on or above the base layer, the multi-layered structure having a sense region therein, the magnetization-bias layers making electrical contact with the magnetic layer, the base layer being composed of zirconium (Zr) or alloy thereof, and (d2) a pair of electrode layers electrically connected to the sense region at its opposite sides, the electrode layers leading a sense current into the sense region at one side thereof and leading the sense current out of the sense region through the other side thereof, each of the electrode layers being formed on each of the magnetization-bias layers.
For instance, the lower and upper shield layers may be composed of a material selected from a group consisting of NiFe, CoZr, CoFeB, CoZrMo, CoZrNb, CoZrTa, CoHf, CoTa, CoTaHf, CoNbHf, CoHfPd, CoTaZrNb, CoZrMoNi, FeAlSi, and iron nitride.
It is preferable that the lower and upper shield layers have a thickness in the range of 0.3 to 10 xcexcn.
It is preferable that the magnetization-bias layers and the electrode layers extend along the magneto-resistive element from its sidewall to its upper surface.
In another aspect of the present invention, there is provided a method of fabricating a magneto-resistive sensor, including the steps of (a) forming a base layer on a substrate so that the base layer has controlled roughness, the base layer being composed of zirconium (Zr) or alloy thereof, and (b) forming a multi-layered structure on the base layer, the multi-layered structure including at least a magnetic layer and a non-magnetic layer.
It is preferable that the base layer is formed through sputtering, and the roughness is controlled by varying a pressure of argon gas.
It is preferable that the roughness is controlled to be equal to or smaller than 2 nm in the step (a).
In still another aspect of the present invention, there is provided an apparatus for magnetically reproducing data, including (a) such a magneto-resistive sensor as mentioned above, (b) a head magnetically recording data into the medium, and formed on the magneto-resistive sensor, (c) a slider sliding on the medium, the magneto-resistive sensor and the head being fixed to the slider, and (d) a device moving the slider to thereby position the magneto-resistive sensor and the head at a predetermined region on the medium.
It is preferable that the head is comprised of (a) a coil generating lines of magnetic force when a current flows therethrough, and (b) lower and upper cores sandwiching the coil therebetween so that the lower and upper coils define a gap between them and the medium, the lower and upper cores directing the lines of magnetic force.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
The inventor considered that the reason why MR sensor including a base layer composed of Ta could not have a high resistance-change ratio was that a base layer composed of Ta had a low mirror reflectivity. Hence, the inventor searched various materials which could provide a base layer with a high mirror reflectivity.
If a base layer were composed of a material having a high mirror reflectivity, other than Ta, crystallinity of MR layer was degraded. However, if a base layer were composed of zirconium (Zr) or an alloy containing Zr therein, it was possible to obtain MR layer having superior crystallinity.
However, if a film composed of Zr or alloy of Zr were deposited by sputtering in an ordinary condition, for instance, if such a film is used as a base layer in a multi-layered structure in a spin-valve effect type MR sensor, a resistance-change ratio in MR sensor is not increased. It was found that the reason why a resistance-change ratio is not increased in MR sensor including a base layer composed of Zr or alloy thereof was that since the base layer had a great surface-roughness, the mirror reflectivity of the base layer remained low in spite of zirconium having a high mirror reflectivity.
In order to overcome this problem, the inventor found out that a surface-roughness of a Zr film could be controlled by controlling a pressure of an argon (Ar) gas when a film composed of Zr or alloy thereof was deposited by sputtering.
In accordance with the results of the experiments the inventor conducted, when a base layer in a multi-layered structure in a spin-valve effect type MR sensor is composed of Zr or alloy thereof, the Zr base layer is designed to have a surface-roughness equal to or smaller than 2 nm. This ensures enhancement in crystallinity in MR layer.
In addition, a mirror reflectivity of conduction electrons is designed to be equal to or greater than 0.1, preferably, 0.2, thereby a resistance-change ratio can be significantly enhanced in comparison with a conventional base layer composed of Ta.
Furthermore, the above-mentioned MR sensor can be incorporated into an apparatus for magnetically reproducing data. This ensures enhancement in reproduction output and improvement in S/N ratio.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.